Growth hormone, prolactin, ACTH, TSH, FSH and LH
Mnemonic
FLAT PIG:
- F - FSH
- L - LH
- A - ACTH
- T - TSH
- P - Prolactin
- I - Ignore
- G - GH
The first four (FLAT) are tropic, acting on other endocrine glands; the last two (PG) act directly on tissues.
The posterior pituitary stores rather than makes its two hormones, ADH and oxytocin, which are synthesised in the hypothalamus.
Prolactin is the only one under tonic inhibition, by dopamine. Two consequences follow: stalk compression raises prolactin (by removing the inhibition), and dopamine antagonists such as antipsychotics and metoclopramide cause hyperprolactinaemia, while dopamine agonists treat it.
The order of loss in progressive pituitary failure is often remembered as GH and gonadotrophins first, ACTH and TSH last, since the last two are life sustaining.
Expansion
Six hormones from five cell types:
- Growth hormone (somatotrophs): growth and metabolism
- Prolactin (lactotrophs): lactation. Uniquely under tonic inhibition by dopamine
- ACTH (corticotrophs): adrenal cortisol
- TSH (thyrotrophs): thyroid hormone
- FSH and LH (gonadotrophs): gonadal function
Control is by hypothalamic releasing hormones delivered through the hypophyseal portal system, so a stalk lesion cuts off all of them.
The prolactin exception is important: because it is normally inhibited by dopamine, a stalk lesion or dopamine antagonist causes prolactin to rise while all other pituitary hormones fall. This is the “stalk effect”, and it distinguishes moderate hyperprolactinaemia from a true prolactinoma, which usually causes much higher levels.
The order of failure in compressive lesions gives a practical clinical sequence, with ACTH deficiency being the most dangerous and requiring replacement before thyroxine, since thyroxine increases cortisol turnover and can precipitate an adrenal crisis.